The invention relates to a projection system for projecting one or more beams on a target, wherein said system is adapted for reducing the influence of residual vibrations on a position of a projection module of the system relative to the target. Such systems are used in applications such a lithography and microscopy, in which one or beams have to be projected onto a target with high accuracy, e.g. within nanometer accuracy.
European Patent application 1 577 929 describes an electron beam exposure apparatus comprising a column for irradiating a sample with an electron beam, a sample chamber having a vacuum pump, a stage arranged within the sample chamber for holding and moving the sample, and a mounting for elastically supporting the column with respect to the sample chamber. By measuring the relative displacement between an upper partition of the sample chamber and the column as well as the acceleration of the column, and then feedback-controlling an actuator which is provided between the upper partition and the column, a high-frequency component of vibration disturbance from the upper partition is prevented from being transmitted to the column.
The known exposure apparatus has a complex construction, e.g. comprising an actuator between the upper partition of the chamber and the column for preventing high frequency vibrations from being transmitted from the chamber to the column. Moreover, due to the elasticity of the mounting, displacement of the column relative to the frame in a first direction will lead to a build up of elastic potential in the mounting, which in turn will provide a restoring force for displacing the column relative to the chamber in a direction opposite to said first direction later on.
US Patent application 2004/0041101 describes an exposure apparatus including a stage for a target, an electromagnetic actuator for moving the stage, a deflector for deflecting electron beams, a laser interferometer for measuring the position of the stage and a controller which controls the electromagnetic actuator on the basis of measurement results obtained by the laser interferometer, wherein the measurement values are provided to the deflector. To some extend, the effect of residual vibrations may thus be compensated for by altering the amount of deflection provided to the electron beams by the deflector. However, by changing the deflection of the electron beams, the angle of incidence with which the beams strike the target surface is changed, as is the projection of said beams on the target.
Moreover, the prior art apparatus requires communication and controls exchange between different subsystems of the exposure apparatus, significantly complicating the design and development thereof, and hence raising costs of such an apparatus. The prior art apparatus requires communication and controls distribution between a target positioning controller, a stage system, a metrology system and a beam projection system, highly complicating the projection of the beams and the design of the apparatus.
It is an object of the present invention to provide a projection system in which the influence of residual vibrations on the projection of beams onto a target is substantially reduced, wherein preferably said projection system has a reduced complexity in view of the above indicated target positioning functionality.